Icy Mystery

So - this morning as we let Cash out we noticed a bizarre sort of icicle sticking UP from Maddox's sand box.
?????????????
We are baffled. There are no wires or trees overhead...simply open sky. It is sticking up at an angle...approximately 5-6 inches tall. It is hollow in the center - holding water. I'd love to hear any theories on this...because I have none. :-)

Check it out...